Additive for inhibiting photolytic degradation reactions in aminoplasts

ABSTRACT

The invention relates to a UV additive for aminoplast resins, to a method for producing a UV additive as well as to uses thereof. Said UV additive contains soluble sterically-hindered nitroxyl compounds in an aqueous aminoplast precondensate. A UV additive for aminoplast resins with several application forms is thus obtained.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to UV additives for amino resins with a nitroxylcompound soluble in an aqueous aminoplastic precondensate, to aUV-resistant amino resin, to a UV-resistant aminoplastic moldingcomposition, to a UV-resistant aminoplastic precondensate, to a processfor producing a UV-resistant laminate, to a process for preparingUV-resistant amino resins, and for preparing UV-resistant aminoplasticmolding compositions.

2. Description of the Related Art

The excellent properties of thermosets, especially amino resins, givesthem outstanding suitability for many applications where demands are,inter alia, scratch resistance, flame retardency, mechanical stability,gloss, environmental compatibility and chemical inertness. From theseapplications, resistance to UV radiation over many years is also needed,since yellowing or yellow coloration of the surfaces is undesirable.Amino resins therefore require addition of suitable UV stabilisers. Veryhigh requirements are placed upon these UV stabilisers suitable foramino resins. They include, for example, good solubility in the aminoresin, since a precondition for their effectiveness is homogeneousdistribution of the UV stabilisers in the resin matrix. Anothercriterion is chemical stability during the curing process characteristicof aminoplastics. Another decisive factor in that there has to belasting binding of the UV stabiliser within the aminoplastics. Thismeans that there must, for example, be no subsequent leaching of thestabiliser out of the aminoplastics. Another decision factor is that UVprotection is active immediately, i.e. as soon as mixing with theaminoplastics has ended. A further decisive factor is that the UVstabilisers do not color aminoplastics but ensure that transparencycontinues over the years.

U.S. Pat. No. 5,629,426 prepares sterically hindered nitroxyl compoundsof 4-hydroxy-2,2,6,6-tetramethylpiperidine type from the underlying4-hydroxy-2,2,6,6-tetramethylpiperidine, which is not a free radical,via an oxidation process with the aid of hydrogen peroxide in thepresence of a carbonate or bicarbonate of ammonium or of an alkali metalas catalyst. One possible use of these nitroxyl compounds is the use aspolymerisation inhibitor to prevent premature polymerisation of vinylmonomers.

U.S. Pat. No. 5,436,345 describes another preparation method. Anapplication sector given is the polymerisation of reactive acrylicmonomers.

EP 0581737 B1 again describes the use of sterically hindered nitroxylcomponents of 2,2,6,6-tetramethylpiperidine type. They are described aspolymerisation inhibitors in the monomer preparation process foraromatic vinyl components (examples being styrene, alpha-methylstyrene,or in other substituted vinylbenzenes).

Compounds of the type represented by ortho-hydroxyphenylbenzotriazoles,2-aryl-2H-benzotriazoles, hydroxyaryl-1,3,5-triazines or sulfonated1,3,5-triazines are also known and are used in textile materials asabsorbers for the UV-A and UV-B components of sunlight, these beinginjurious to the skin. According to EP 0659877 A2, the sun-protectionfactor of clothing can be increased by adding these compounds to therinsing water for a textile material, for example. The UV absorbers arein aqueous solution, or if water-solubility is poor, in disperse formwhen incorporated into the textile material.

There are no UV additives known hitherto which fulfil the requirementsfor amino resins. The properties of the additives known forthermoplastics are inadequate for aminoplastics. EP 0704560 B1, forexample, describes a synergistic combination of UV absorbers from theortho-hydroxyphenylbenzotriazoles group with a sterically hindered amine(HALS, hindered amine light stabiliser) from the2,2,6,6-tetramethylpiperidine compounds group, for UV protection ofthermoplastic fibres. These UV stabilisers cannot be used foraminoplastics, since they cannot be incorporated homogeneously intoaminoplastics.

Furthermore, they have the disadvantage that the substance responsiblefor the UV protection has to be formed in situ, not until exposure to UVlight has begun. This means that there is a time delay in the protectiveaction with respect to UV irradiation.

The object of the present invention was to provide a UV additive foramino resins.

DETAILED DESCRIPTION OF THE INVENTION

For the purposes of the present invention, amino resins are resins whichcontain, as amine component, melamine, urea, dicyandiamide, cyanamide,guanamine, sulfonamide, aniline, or substituted melamines and urea ormixtures of these components. Preferred amino resins are melamineresins, urea resins or melamine-urea resins.

As carbonyl compound, the amino resins preferably contain aldehydes ofchain length C1-C10 or mixtures of this chain length derived fromvarious aldehydes, examples being formaldehyde, acetaldehyde,trimethylolacetaldehyde, acrolein, benzaldehyde, furfural, glyoxal,glutaraldehyde, phthalaldehyde, terephthalaldehyde, isobutyraldehyde,acetone, or ketones, for example methyl ethyl ketone and diethyl ketone.It is particularly preferable to use formaldehyde. Amino resins may alsohave been etherified, for example with methanol, and the amino resinshere have preferably been partially etherified. They may, whereappropriate, also comprise modifiers, such as plasticisers.

Amino resins are further processed in the form of aqueous solutions,known as aqueous aminoplastic precondensates. The aqueous aminoplasticprecondensates usually comprise additives, such as hardeners, wettingagents, or release agents.

The sterically hindered nitroxyl compound of the invention is soluble inan aqueous aminoplastic precondensate. It belongs to the hindered aminelight stabiliser (HALS) group and is in particular a2,2,6,6-tetramethylpiperidine-N-oxyl compound having a functional group.

It is particularly preferable to use4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy as nitroxyl compound.

Examples of HALS compounds are piperidine compounds and N-oxylderivatives of piperidine compounds.

Examples of UV absorbers are 2-hydroxybenzophenone derivatives,hydroxyphenylbenzotriazole derivatives, hydroxyphenyl-s-triazinederivatives, cinnamic acid derivatives and/or oxalanilides. Preferenceis given to 4-hydroxytetramethylpiperidine and/or 4-aminotetramethylpiperidine, particular preference is given tobis(2,2,6,6-tetramethyl-1-(octyloxy)-4-piperidinyl sebacate and/oretherified piperidine compounds, and alsoN,N′-diformyl-N,N′-di(1-oxylradical-2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine,4-amino-2-hydroxybenzophenone, 2-hydroxy-4-sulfobenzophenone and/or2,4-dihydroxybenzophenone, 2-(2,4-dihydroxyphenyl)-2-H-benzotriazoleand/or 2-(2-hydroxy-4-sulfo)-2-H-benzotriazole, particularly preferably(α-[3-[-(2H-benzotriazol-2-yl)-5-(1,1,-dimethylethyl)-4-hydroxyphenyl-1-oxopropyl]-ω-hydroxypoly(oxo-1,2-ethanediyl)and/or sodium3-(2H-benzotriazol-2-yl)-5-sec-butyl-4-hydroxybenzenesulfonate,2-(2-hydroxyphenyl)-4,6-(4-sulfophenyl)-1,3,5-triazine and/or4,6-(4-aminophenyl)-2-(2-hydroxyphenyl)-1,3,5-triazine,3-(4-hydroxyphenyl)propenecarboxylic acid and/or3-(4-hydroxyphenyl)-2-methylpropenecarboxylic acid,N,N′-(2-hydroxyphenyl)ethanediamide and/orN-(2-hydroxyphenyl)-N′-(4-sulfophenyl)ethanediamide.

UV absorbers may be used together with the substance of the invention,for example. One possible quantitative proportion of the substance ofthe invention to UV absorber is from 5:1 to 1:5. A preferred range isfrom 1:1 to 1:5.

Within the nitroxyl compound, the functional group is preferably in thepara position with respect to the N-oxyl group. Examples of functionalgroups are hydroxy groups or amino groups, ammonium salts, ethyleneoxide groups or propylene oxide groups, ethylene oxide-propylene oxidecopolymers or carboxylates. Possible cations here are sodium, calcium ormagnesium, and chlorides are an example of possible anions.

In addition to the nitroxyl compound, a HALS compound which is not afree radical may be present in the UV additive of the invention. ThisHALS compound which is not a free radical preferably derives from thesame group of substances as the nitroxyl compound, the difference beingthat the oxy radical has been replaced by a functional group, such as anH group, ether, acyl group, alkyl group, or a hydroxy group.

However, it is also possible to use any desired hydrophobic HALScompounds which are not free radicals, for example in the form ofaqueous dispersions, as long as they comply with the requirements foramino resins with regard to acid/base properties and can be incorporatedinto the amino resin with the desired homogeneity.

Besides the nitroxyl compound of the invention, there is a substituted1,3,5-triazine or a UV absorber from theortho-hydroxyphenylbenzotriazoles group soluble in an aqueousaminoplastic precondensate present in the UV additive of the invention.From the triazines group mention may particularly be made here ofhydroxyaryl-1,3,5-triazine. Substituted here means generally thepresence of an additional chemical group (e.g. functional group, organicmoiety). This definition includes hydrogen as substituent.

The UV absorber preferably derives from theortho-hydroxyphenylbenzotriazoles group. Theortho-hydroxyphenylbenzotriazole advantageously contains a functionalgroup and an organic moiety. The functional group here is preferably inthe para position with respect to the OH group, and the organic moietyis preferably in the ortho position with respect to the OH group.

Advantageous embodiments of organic moieties are alkyl moieties oflength C₁-C₁₂ or aryl moieties. Preference is given to alkyl moieties ofchain length C₁-C₅, and particular preference is given to C₄ ⁻alkylmoieties, such as secondary butyl moieties. Examples of functionalgroups are ethylene glycol groups, polyethylene glycol groups orpolyvinyl alcohol groups or ethylene oxide, propylene oxide, ethyleneoxide-propylene oxide copolymers or carboxylates.

Advantageous embodiments of functional groups are salts, the preferredsalts being sulfates, sulfonates or ammonium salts. Examples of apossible cation are sodium ions, calcium ions or magnesium ions, andchlorides are examples of possible anions.

In one particularly advantageous embodiment, the UV absorber has an SO₃⁻ group on an ortho-hydroxyphenylbenzotriazole. A particularly preferredUV absorber is sodium3-(2H-benzotriazole-2-yl)-5-sec-butyl-4-hydroxybenzenesulfonate.

If the UV absorber derives from the substituted 1,3,5-triazines group,it preferably contains an organic moiety, which is preferably in themeta position with respect to the functional group.

If the UV absorber derives from the hydroxyaryl-1,3,5-triazines group,it preferably contains a functional group and/or one or more organicmoieties. The functional group here is preferably in the meta positionwith respect to the OH group and the organic moiety/moieties on thetriazine ring.

Examples of functional groups and organic moieties for the substituted1,3,5-triazines group are the same as those for the UV absorbers fromthe ortho-hydroxyphenylbenzotriazoles group.

The amount of UV absorber is advantageously higher than the amount ofnitroxyl compound. The amount of UV absorber is from about 1 to 5% byweight, preferably from 1 to 3% by weight, particularly preferably from1 to 2% by weight, based on the solid amino resin.

The amount of nitroxyl compound of the invention in the UV additive isfrom about 0.1 to 3% by weight, preferably from about 0.1 to 2% byweight, particularly preferably from about 0.1 to 1% by weight, based onthe solid amino resin.

In one preferred embodiment, the UV additive is added during thesynthesis of an amino resin. This is a UV-resistant liquid amino resinwhich is then spray-dried. This gives a UV-resistant solid amino resin.

This solid resin may then be transported and/or stored. It is notdissolved in water until shortly prior to laminate production, and canbe used for impregnating a sheet.

In another advantageous embodiment, the UV additive is added to anaminoplastic melt during the synthesis of an aminoplastic moldingcomposition. This gives a UV-resistant aminoplastic molding compositionor a UV-resistant pelletized material.

The nitroxyl compound of the invention is used to produce UV-resistantlaminates from amino resins, for example.

For the production of the laminates, the UV additive is mixed with anaqueous aminoplastic precondensate whose strength is from about 30 to70%, preferably from about 50 to 60%, based on the amount of the solidamino resin, giving an aqueous, UV-resistant aminoplastic precondensate.

Where appropriate, additives are added, examples being wetting agents orrelease agents and plasticisers and also hardeners.

A dry absorbent sheet is then impregnated with this aqueous,UV-resistant aminoplastic precondensate.

For the purposes of the invention, the absorbent sheet preferablycomprises cellulose and/or lignocellulose, and takes the form of paper,paperboard, fabric or nonwoven, wood veneers, wood-fibre boards orwood-chip boards.

The resultant sheet impregnated with the aqueous, UV-resistantaminoplastic precondensate is dried prior to further processing. It ispossible here for the dried sheet to be saturated again with theaqueous, UV-resistant aminoplastic precondensate and then dried again. Adecisive factor is that drying has to take place prior to the furtherprocessing of the impregnated sheet. The amount of aminoplasticprecondensate applied, based on the sheet initially used, is from about40 to 200% by weight, preferably from about 100 to 170% by weight,preferably from about 120 to 140% by weight.

One or more of these impregnated and dried sheets are then press-molded,for example, to give a multilayer laminate, and thus fully cured.

It is also possible for the press-molding to be carried out using one ormore intermediate layers, such as core papers, or one or more carriermaterials, such as press chipboards.

The resultant UV-resistant laminate has outstanding UV resistance andmay be used either for outdoor or indoor applications, for example forfurniture surfaces, floorcoverings, or facades.

In another advantageous embodiment, the UV additive is added to anaminoplastic melt during the synthesis of an aminoplastic moldingcomposition. This gives a UV-resistant aminoplastic molding compositionor a UV-resistant pelletized material.

An advantage of the UV additive of the invention is that it can beincorporated homogeneously into the aqueous aminoplastic precondensate,thus reliably providing uniform distribution, also in the finishedlaminate. Another advantage is stability during the characteristiccuring process for aminoplastics under acidic conditions and at anelevated temperature. In addition, covalent bonds are formed between theUV absorber or the nitroxyl compound of the UV additive and theaminoplastics, resulting in immobilisation of the UV additive in theaminoplastic, and thus preventing subsequent leaching, for example inoutdoor applications, even in the long term.

All of these properties of the UV additive of the invention ensure longlasting and uniform UV protection of the aminoplastics.

Another advantage of the UV additive of the invention is immediateprotection with respect to exposure to UV radiation, since the activesubstance responsible for the protective action, in the form of thefree-radical nitroxyl compound, is directly present in its active form.In contrast to this, UV-protective action using the known HALS compoundswhich are not free radicals, which form the active free-radicalsubstance in situ only after exposure to UV radiation has begun,involves a time delay because the in-situ reaction requires a certaintime.

Unexpectedly, the sheet impregnated with the UV additive of theinvention and dried still has the acquired colorless and transparentsurface, as has the laminate produced therefrom.

For laminates it is important that these can be obtained with thespecific desired coloring, this usually being the color of the uppermostply of the sheet. This means that the laminate surface has to becolorless and transparent, and that therefore the UV additive must notcause any coloring of the laminate surface.

Unexpectedly, this requirement is complied with when using the UVadditive of the invention, although the nitroxyl compound present in theUV additive has a strong color.

The preferred nitroxyl compound4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy has a deep orange color, forexample. The UV additive of the invention comprising the nitroxylcompound also has this intense color.

Unexpectedly, the sheet retains its original color both during theimpregnation with the colored UV additive and during subsequentprocessing, and the UV-resistant laminate obtained after press-moldingand curing therefore has the required colorless and transparent surface.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments of the invention are described below by way of example.

FIG. 1 shows the structural formula of theortho-hydroxyphenylbenzotriazole with substituents;

FIGS. 2 a-c show structural formulae of the triazines with a moiety(FIG. 2 c);

FIG. 3 shows the structural formula of the free-radical nitroxylcompound;

FIG. 4 shows the structural formula of the HALS compound which is not afree radical.

Compounds according to FIG. 1 are ortho-hydroxyphenylbenzotriazolecompounds according to the teaching of the invention.

R1 here may be:

-   -   alkyl moieties of C₁-C₁₂    -   aryl moieties

R2 may be:

-   -   SO₃ ⁻ (in the form of Na salt, Ca salt or magnesium salt)    -   sulfonate    -   sulfate    -   CH₂COO (carboxylate)    -   CH₂NH₃ ⁺Cl⁻ (ammonium)    -   (CH₂—CH₂—O—)_(x)H (ethylene oxide)    -   propylene oxide    -   CH₂—(O—CH₂—CH₂)_(x)—OH ((poly)ethylene glycol)    -   ethylene oxide-propylene oxide copolymers    -   CH₂—(CH₂—CHOH—)_(x)—OH polyvinyl alcohols    -   CH₂—COO⁻Na⁺

The compounds shown in FIG. 2 a-c belong to the 1,3,5-triazines class.The possible substituents for R1 and R2 have been described above in thecontext of FIG. 1. R3 is one of the following moieties.

Hydroxyphenyl having R1 substituents, the moiety R1 having beendescribed above in the context of FIG. 1.

FIG. 3 shows free-radical nitroxyl compounds of hindered amine lightstabilizer type, HALS.

R4 here is one of the following moieties:

-   -   NH₂ (amino)    -   NH₃ ⁺Cl⁻ (ammonium)    -   (CH₂—CH₂—O—)_(x)H (ethylene oxide)    -   propylene oxide    -   ethylene oxide-propylene oxide copolymers    -   CH₂COO⁻ (in the form of Na salt, Ca salt or Mg salt)        (carboxylate)    -   OH (hydroxy)

FIG. 4 shows HALS compounds which are not free radicals.

R5 here is one of the following moieties, and R within these moieties isa carbon chain of length C₁-C₁₂:

-   -   H (hydrogen)    -   OR (ether)    -   COR (acyl)    -   R (alkyl)    -   OH (hydroxy)

Two preparative examples are given below.

EXAMPLE 1

500 g of melamine-formaldehyde resin are dissolved in 500 g of water,and then 3 g of the wetting agent Melpan Nu 117 and 6 g of the hardenerMelpan A 462 are added. The nitroxyl compound4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy and the UV absorber sodium3-(2H-benzotriazol-2-yl)-5-sec-butyl-4-hydroxybenzenesulfonate are addedto this aqueous aminoplastic precondensate. The resultantyellow-orange-colored mixture is stirred until a clear yellow-orangecolored solution is obtained.

White decorative-grade paper (density 80 g/m²) is impregnated with thissolution. The impregnated decorative-grade paper which, surprisingly,has its initial color after impregnation, is then dried for 20 secondsat 140° C. The dried paper is impregnated a second time with theyellow-orange colored solution comprising the nitroxyl compound andcomprising the UV absorber, and then again dried at 140° C. to aresidual moisture level of from about 6 to 7% by weight. This doubleimpregnation gives a total resin application of 150% by weight, based onthe weight of the dry white decorative-grade paper initially used. Theresultant impregnated paper has the same color as the unimpregnatedpaper initially used. This means that the cured aminoplasticprecondensate comprising UV stabilisers complies with the requirementfor colorless transparency.

The resultant impregnated decorative-grade paper is press-molded withfour plies of a core paper impregnated with melamine-formaldehyde resinwithout UV stabiliser, and with a balancing paper likewise impregnatedwith melamine-formaldehyde resin without UV stabiliser, to give amultilayer laminate. The press-molding conditions used here are asfollows: press-molding time 2 min, press-molding temperature 150° C.,press-molding pressure 80 kg/cm². After subsequent cooling to 70° C.,the laminate is removed from the press.

The resultant laminate has a colorless and transparent surface.

The UV resistance of this resultant UV-resistant laminate is measuredand compared with a laminate without UV stabiliser. The laminate withoutUV stabiliser was produced in the same way as the UV-resistant laminateexcept that the papers used were impregnated with melamine-formaldehyderesin without UV stabiliser.

For measuring UV resistance, the change in the infrared spectrum of thelaminate brought about by exposure of the amino resin to UV light wasused as a measure of UV resistance. The change in the spectrum herebecomes greater as the UV resistance of the particular laminate becomespoorer. An IR spectrum is recorded for both laminates. A dry-weatheringtest is then carried out, simulating 336 hours of exposure of bothlaminates to UV light, and the IR spectrum of both laminates is thenrecorded again and the change in each spectrum is evaluated.

The change in the IR spectrum of the UV-resistant laminate was 0.08absorption units, whereas that for the laminate without UV stabiliserwas 0.23 absorption units.

EXAMPLE 2

A method similar to that of Example 1 was used to impregnate browndecorative-grade paper with the same yellow-orange solution comprisingthe nitroxyl compound and the UV absorber. The paper was then dried for1 hour in air and then for 90 seconds at 120° C. in a drying cabinet,until the residual moisture level was about 8% by weight. This singleimpregnation gave a total resin application of 140% by weight, based onthe weight of the dry brown decorative-grade paper initially used.

Using a method similar to that of Example 1, a multilayer laminate wasproduced from this impregnated paper, four core papers and a balancingpaper, and had a transparent surface.

After the IR spectra had been recorded, this UV-resistant laminate wassubjected, together with a brown-decorative-paper laminate without UVstabiliser, to a wet-weathering test stimulating 1500 hours of exposureto UV light. An IR spectrum was again recorded for both laminates.

The change in the IR spectrum of the UV-resistant laminate was 0.04absorption units, whereas that of the laminate without UV stabiliser was0.18 absorption units.

In the optical test local color-lightening was found for the laminatewithout UV stabiliser, and moreover, marked loss of gloss and yellowingwere discernible. In contrast to this, no change could be determinedvisually for the UV-resistant laminate.

1. A UV additive for amino resins comprising a water soluble, stericallyhindered nitroxyl compound soluble in an aqueous aminoplasticprecondensate and a UV absorber soluble in an aqueous aminoplasticprecondensate, wherein the UV absorber comprisesortho-hydroxyphenylbenzotriazoles according to formula I

wherein R1: is alkyl moieties of length C₁-C₁₂, or aryl moieties, R2: isSO₃ ⁻ (in the form of Na salt, Ca salt or magnesium salt), sulfonate,sulfate, CH₂COO⁻(carboxylate), CH₂—NH₃ ⁺Cl⁻ (ammonium),(CH₂—CH₂—O—)_(x)H (ethylene oxide), propylene oxide,CH₂—(O—CH₂—CH₂—)_(x)—OH ((poly)ethylene glycol), ethyleneoxide-propylene oxide copolymers, CH₂—(CH₂—CHOH—)_(x)—OH polyvinylalcohols, or CH₂—COO⁻Na⁺.
 2. The UV additive as claimed in claim 1,wherein the nitroxyl compound is a 2,2,6,6-tetramethylpiperidine N-oxylcompound.
 3. The UV additive as claimed in claim 1, wherein the nitroxylcompound is 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy.
 4. The UVadditive as claimed in claim 1, wherein the nitroxyl compound comprisesammonium salts, carboxylates, hydroxy groups, amino groups, ethyleneoxide groups, propylene oxide groups, or ethylene oxide-propylene oxidecopolymers.
 5. The UV additive as claimed in claim 1, further comprisingan additional sterically hindered amine which is not a free radical. 6.The UV additive as claimed in claim 5, wherein the sterically hinderedamine which is not a free radical contains, as a substituent, an ethergroup, acyl group, alkyl group, hydroxy group, or hydrogen.
 7. The UVadditive as claimed in claim 1, wherein a substituent for a substancefrom the ortho-hydroxyphenylbenzotriazoles group is at least one of afunctional group which has been arranged in para position with respectto the OH group and an organic moiety which has been arranged in orthoposition with respect to the OH group.
 8. The UV additive as claimed inclaim 1, wherein the UV absorber contains, as a functional group, atleast one carboxylate, ethylene glycol, polyethylene glycol group,polyvinyl alcohol group, ethylene oxide group or propylene oxide group,or contains, as organic moieties, at least one aryl moiety or alkylmoiety of length C₁-C₁₂, in particular one of chain length C₁-C₅,preferably alkyl moieties of length C₄ or contains both.
 9. The UVadditive as claimed in claim 1, wherein the UV absorber is present insalt form, in particular as sulfate, sulfonate or ammonium salt.
 10. TheUV additive as claimed in claim 1, wherein the UV absorber comprisesethylene oxide-propylene oxide copolymers.
 11. The UV additive asclaimed in claim 1, wherein the UV absorber contains a SO₃ group on anortho-hydroxyphenylbenzotriazole.
 12. The UV additive as claimed inclaim 1, wherein the UV absorber is sodium3-(2H-benzotriazol-2-yl)-5-sec-butyl-4-hydroxybenzenesulfonate.
 13. TheUV additive as claimed in claim 1, wherein the UV absorber derives froma group of the ortho-hydroxyphenylbenzotriazoles, in particular havingat least one substituent.
 14. The UV additive as claimed in claim 13,wherein a functional group is in para position with respect to the OHgroup and the organic moiety is in the ortho position with respect tothe OH group.
 15. The UV additive as claimed in claim 1, wherein theamino resins are melamine resins, urea resins, or melamine-urea resins.16. The UV additive as claimed in claim 1, wherein the proportion of theUV absorber is higher than the proportion of the nitroxyl compound,where the proportion of UV absorber is from about 1 to 5% by weight, inparticular from 1 to 3% by weight, preferably from 1 to 2% by weight,based in each case on the solid amino resin.
 17. The UV additive asclaimed in claim 1, wherein the amount of nitroxyl compound is fromabout 0.1 to 3% by weight, in particular from 0.1 to 2% by weight,preferably from 0.1 to 1% by weight, based in each case on the solidamino resin.
 18. A UV-resistant amino resin comprising a UV additive asclaimed in claim
 1. 19. A UV-resistant aminoplastic molding compositionor UV-resistant pelletized material or both comprising a UV additive asclaimed in claim
 1. 20. A UV-resistant aminoplastic precondensatecomprising a UV additive as claimed in claim
 1. 21. The UV-resistantaminoplastic precondensate as claimed in claim 20, comprising from about30 to 70% by weight, in particular from 50 to 60% by weight, based onthe amount of the solid amino resin, of the UV additive of theinvention.
 22. An absorbent sheet saturated with a UV-resistantaminoplastic precondensate as claimed in claim 20 and dried.
 23. Thesheet as claimed in claim 22, wherein the absorbent sheet preferablycomprises cellulose or lignocellulose or both.
 24. A UV-resistantlaminate which comprises at least one fully cured sheet as claimed inclaim
 22. 25. A process for producing a UV-resistant laminate as claimedin claim 24, wherein at least one sheet is saturated with anaminoplastic precondensate which with UV additive is dried, whereappropriate, with at least one intermediate layer and, whereappropriate, with at least one carrier material, is press-molded andfully cured.
 26. The process as claimed in claim 25, wherein the amountof aminoplastic precondensate applied, based on the sheet initiallyused, is from about 40 to 200% by weight, in particular from 100 to 170%by weight, preferably from 120 to 140% by weight.
 27. A process forpreparing a UV-resistant amino resin, comprising the step of adding a UVadditive as claimed in claim 1 during the synthesis of the amino resin.28. A process for preparing a UV-resistant aminoplastic moldingcomposition or for preparing a pelletized material, comprising the stepof adding a UV additive as claimed in claim 1 to an aminoplastic meltduring the synthesis of the aminoplastic molding composition.